A technique for manufacturing a desired three dimensional molded body is well known by, for example, U.S. Pat. No. 5,273,698. In that patent, it is disclosed that a method for manufacturing a three dimensional molded body comprises the steps of: uniformly coating a liquid reactive mixture of a urethane foam; and compressing the mixture for a certain period by use of means of an upper mold and a lower mold when a gas reaction thereof has been completed but the mixture is still in a visco-elastic flowing condition. Such a conventional technique is widely applied for seats of chairs or cars, articles relevant to the apparel industry such as a T-shirt, a cap or a bag and the like.
In general, a urethane is foamed by chemically reacting a mixture which comprises mainly two liquids. The mixture often used comprises isocyanate (ISO) and polyol (POL) as main components thereof and a catalyst and water as additional components thereof. Those components produce a foamed polyurethane or a foamed polyurea by foaming the mixture thereof and are, in fact, used for an integrated molding. As mentioned in the above U.S. Patent, the chemical reaction can be divided by two chemical reactions such as a gasification reaction which produces CO.sub.2 and a solidification reaction. A foamed polyurethane is firstly expanded rapidly by the gasification reaction so that the volume thereof is expanded. When this gasification reaction is completed, the whole of the urethane is transformed into a solid condition through a gel condition. An integrated molding must be carried out when the gasification reaction thereof has been completed but the urethane is still in a visco-elastic flowing condition (this period is called as a tack free).
It is desirable to uniformly coat the foamed polyurethane over an object to be compressed. If such a coating is not uniform, a portion at which the gasification reaction is not completed will remain when compressing in an upper mold and a lower mold and a product will be cracked. Thus, in order to coat the urethane foam uniformly, a resilient sheet has been used in the art. Such a resilient sheet must be excellent in the resiliency and the durability, and this is because the foamed polyurethane is coated on the resilient sheet and is compressed together with the resilient sheet between the upper mold and the lower mold.
As disclosed in the aforementioned reference, a polyethylene film and the like is used as such a resilient sheet in the art. However, the polyethylene film is poor in stretchability. That is, once the film is elongated, the elongated film is not restored into the original state and is thinned so that the film can be broken. Also, the polyethylene film is poor in a separating ability from a mold i.e. the polyethylene sheet is not easily separated from the mold or the urethane after completing the integrated molding. Moreover, the running cost becomes higher because the durability is poor and the working efficiency is reduced because it takes a long time for replacing.
Meanwhile, as aforementioned, in fact, it is very difficult to rapidly compress in the tack free condition. The starting time of the tack free is different between a portion initially coated and a portion later coated, because the gasification reaction is started during the foamed polyurethane is uniformly coated thereon. Such a reaction time lag makes difficult to take a pressurizing timing. In particular, this time lag is considerable when coating over a wide area. Thus, a method of preheating a liquid mixture of a urethane is idealized in order to accelerate the gasification reaction by reducing the viscosity of polyurethane to shorten the coating time, however, such a hot foamed polyurethane can not be used directly to the aforementioned polyethylene film which is poor in thermal resistance.
The present invention is made in order to overcome those disadvantages of the resilient sheet used in the art.
Therefore, an object of the present invention is to provide a method of an integrated molding by use of a silicone rubber which is excellent in resiliency, stretchability, restoring ability into an original state and separating ability from a mold.
Another object of the present invention is to reduce a running cost and to improve a working efficiency by using a silicone rubber which has a high durability.
Still another object of the present invention is to provide a method of an integrated molding in which a pressurizing time can be easily taken by using a silicone rubber which has a high thermal resistance.